Integrated Circuit Temperature Measurement Methods and Apparatuses

ABSTRACT

Methods and apparatuses to measure temperatures of integrated circuits are disclosed. New circuit arrangements for measuring temperature using various types of integrated circuit sensor elements are discussed. Embodiments comprise methods and apparatuses arranged to measure temperature based upon current leakage rates of different integrated circuit sensor elements. The methods and apparatuses generally involve using a pulse module to generate a charge for the integrated circuit elements. In these method and apparatus embodiments, one or more elements form a decay module to sense when the voltage decays to a threshold value. The method and apparatus embodiments may also have a module to calculate or infer a temperature from the rate of the voltage decay.

FIELD

The present invention generally relates to the field of temperaturemeasurement. More particularly, the present invention relates tomethods, apparatuses, and systems to measure temperature in integratedcircuits.

BACKGROUND

Designers generally increase performance of integrated circuits byincreasing operating frequencies of the circuits and by increasing thenumber of components, such as transistors, in the circuits. To keepcircuit sizes manageable, designers have reduced or scaled down the sizeof the circuit components so that larger numbers of devices fit withinsmaller per unit areas. Today it is not uncommon to find advancedcomputer system chips containing millions, sometimes billions, oftransistors. This increased density, however, has created numerousproblems. One major problem is heat. Since individual electroniccomponents, such as transistors, each generate minute quantities of heatwhile operating, increased numbers of such devices in the newer circuitsnaturally lead to increased quantities of heat.

Compounding the problem of heat is the desire for designers tocontinually shrink the size of devices containing integrated circuits.For example, designers continually strive to make laptop computers andPersonal Digital Assistant (PDA) devices smaller, thinner, and lighter.However, as the cases of these devices shrink, so too do the amounts ofavailable surface areas used for cooling and heat dissipation. Provencircuit designs, based on older and larger circuit platforms, may starthaving temperature-related problems when they are migrated to differentplatforms having reduced surface areas for cooling.

Heat and high operating temperatures in integrated circuits cause manyproblems. First, higher operating temperatures tend to change theoperating characteristics of integrated circuits. Second, whenintegrated circuits are operated at high temperatures for extendedperiods of time, the long-term reliability of the integrated circuitsusually decrease. With these concerns of decreased performance anddecreased reliability, coupled with the need of increased componentdensity and smaller packaging, designers increasingly need to monitorthe temperature of integrated circuits, including high-performancemicroprocessors and densely populated application specific integratedcircuits (ASICs).

Designers often attempt to manage the temperature of an integratedcircuit (IC) by regulating the speed at which it operates. For example,a designer may try to reduce the temperature of a high-performancemicroprocessor by reducing its operating frequency. Additionally, thedesigners of an IC may protect the circuit from heat-related damage byeither increasing the speed of a cooling fan or possibly shutting downor cutting the circuit off. In order to manage and control thetemperature in these different situations, designers must incorporateeither external sensors or on-chip sensors that measure temperature.

Using on-chip sensors to measure real-time temperatures helps ensureintegrated circuits operate within safe thermal zones. Since manyintegrated circuits today are becoming increasingly complex, withmillions of transistors located within numerous regions of the circuit,designers often desire to know the temperature of several spots in thosenumerous regions. Until recent times most temperature sensors were basedon analog complimentary metal-oxide semiconductor (CMOS) circuits.Temperature measurement with such circuits usually required matchedtransistors. Additionally, these circuits could not be reliablyimplemented in numerous spots in integrated circuit designs.Consequently, designers implemented such sensors sparingly, usuallylimiting the number of sensors to one or two in a given circuit.

Many conventional temperature sensors use analog devices, such asdifferential amplifiers, that transform or convert the analogtemperature signals to digital signals. For example, a large number ofexisting sensors emit either a current or frequency signal that isproportional to temperature. A frequency output requires acurrent-to-frequency converter. Unfortunately such converters tend torequire large amounts of real estate in an integrated circuit, makingsuch technology a poor choice for designers wanting to make numeroustemperature measurements without large circuit footprints.

Designers sometimes use another type of sensor, known as aring-oscillator sensor, for on-chip temperature measurement.Unfortunately, the ring-oscillator sensor also requires a large amountof integrated circuit substrate space. Plus, the ring-oscillator sensorprovides relatively low accuracy. Recently, four-transistor (4-T) decaysensors were proposed. The 4-T sensors are based on a closed-loopprocess which creates a frequency proportional to temperature. However,the suitable operating temperature range is from +30 to +140 degreesCentigrade.

In light of the growing problem of heat and increased operatingtemperatures in high-performance integrated circuits, what are neededare alternative methods and apparatuses to measure temperatures ofintegrated circuits. Alternative temperature sensors need to providerelatively accurate temperature measurements which do not require largefootprints.

SUMMARY

The problems identified above are in large part addressed by new methodsand apparatuses for measuring temperature in integrated circuits, whichinclude processor integrated circuits. One method embodiment generallyinvolves charging one or more transistors in a transistor pair where oneof the transistors has a substantially constant bias voltage, measuringa rate of voltage decay of the transistor or transistor pair, andcalculating a temperature based upon the rate of voltage decay. Themethod may also include applying high and low voltages to a gate of oneof the transistors to switch the transistor on and off to create thevoltage charge for the decay measurement. Alternative embodiments of themethod comprise applying a series of pulses to a gate of one of thetransistors. An alternative embodiment involves calculating thetemperature by counting a series of decay times from a series of pulses.

Another embodiment comprises an apparatus for measuring temperature inan IC. The apparatus generally comprises using a pulse module to chargea node associated with two IC elements and a decay module for measuringa rate of decay of the charged node. The apparatus includes atemperature calculator to calculate a temperature based upon the rate ofdecay. One embodiment of the apparatus may use a pair of CMOStransistors for the IC elements. Another embodiment of the apparatus mayuse a flip-flop to create the pulses. Some embodiments comprise using aSchmitt trigger to detect the voltage decay. Other embodiments may use avoltage comparator to detect the voltage decay.

A further embodiment is an IC arrangement that may be used to measuretemperature. The IC arrangement comprises a p-FET and an n-FETtemperature sensor, a pulse circuit, a voltage drop circuit, and acounter circuit. Some embodiments may use a flip-flop in the pulsecircuit. Some embodiments use a Schmitt trigger coupled to a flip-flopto form the pulse circuit.

An even further embodiment is a system capable of measuring temperaturein a component of the system. Generally, the system may comprise a powersupply, an IC, and a temperature sensor made with two transistors, acharging circuit, a voltage sensing circuit, and a timing circuit. Someembodiments may include a computation module to calculate a temperaturemeasurement based upon the decay time. Some embodiments may exist ascellular telephones or portable computing devices, while otherembodiments may exist as desktop and rack-mounted computing devices,video display cards, portable and non-portable multimedia systems, andASICs.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention will become apparent upon reading the followingdetailed description and upon reference to the accompanying drawings inwhich, like references may indicate similar elements:

FIG. 1 depicts a system comprising a central processing unit, memory, avideo card, bus controllers, and peripheral devices incorporatingnumerous integrated circuit element temperature sensors;

FIG. 2 illustrates how numerous parts of an integrated circuit, such asan integrated circuit in a chip, may incorporate temperature sensors tomeasure different temperatures of the chip;

FIG. 3 shows an embodiment of system employing a transistor temperaturesensor for measuring temperature, comprising a power supply, a pulsemodule, a decay module, and a temperature calculator;

FIG. 4 illustrates a circuit to measure temperature using twotransistors, comprising a Schmitt trigger, a toggle flip-flop, and acounter; and

FIG. 5 depicts a flowchart of a method to measure temperature in anintegrated circuit by increasing the voltage of a node coupled to twotransistors and measuring the rate of decay to calculate thetemperature.

DETAILED DESCRIPTION OF EMBODIMENTS

The following is a detailed description of example embodiments of theinvention depicted in the accompanying drawings. The example embodimentsare in such detail as to clearly communicate the invention. However, theamount of detail offered is not intended to limit the anticipatedvariations of embodiments; but, on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the present invention as defined by the appendedclaims. The detailed descriptions below are designed to make suchembodiments obvious to a person of ordinary skill in the art.

Generally speaking, methods, apparatuses, and techniques to measuretemperature in integrated circuits are disclosed. New transistor sensorand circuit arrangements for various types of integrated circuits,including high-performance processor circuits, are discussed.Embodiments comprise methods, apparatuses, circuits, and systems tomeasure temperature in integrated circuits by charging integratedcircuit elements and measuring the rate of charge decay to calculatetemperature. The embodiments generally involve using pulse modules tocharge the transistor arrangements, wherein one or two transistors arecharged. In these embodiments, a decay module may be used to monitor therate of decay of the charge created by the pulse module. The rate ofdecay of the charge may be directly related to the temperature. In otherwords, the charge may dissipate more rapidly as the temperatureincreases. Upon measuring the rate of decay, therefore, one maycalculate a temperature of the IC.

While portions of the following detailed discussion describe manyembodiments comprising CMOS field effect transistors (FETs), upon reviewof the teachings herein, a person of ordinary skill in the art willrecognize that the following invention may be practiced and appliedusing a variety of IC devices, such as by using junction or unijunctiontransistors, as well as other metal-oxide-semiconductor devices. Allmethods and apparatuses of practicing the invention may beinterchangeable. Further, some discussions for embodiments describegenerating the voltage charge by using a toggle flip-flop triggered by aSchmitt trigger while other embodiments describe using a voltagecomparator to trigger another type of bistable device. One of ordinaryskill in the art will recognize that such devices and circuit elementsare often interchangeable and may produce essentially similar or thesame results. Such terms and devices as these and others should beconsidered to be substituted for the described elements when employed inaccordance with similar constraints to perform substantially equivalentfunctions.

Turning now to FIG. 1, we see an embodiment of a system 100 illustratinghow IC element temperature sensors, such as two-transistor (2-T)temperature sensors, may be placed throughout system 100 to measurenumerous temperature spots. For example, system 100 may comprise adesktop computer motherboard attached to several peripheral devices,wherein IC element temperature sensors may be located throughout thecomputer to monitor the temperatures of different parts of the system.System 100 has a central processing unit (CPU) 105 coupled to cachememory 110 via a backside bus 108. Additionally, a frontside bus 117couples CPU 105 to a bus controller 120. Bus controller 120 may providea gateway for CPU 105 to send and retrieve data from other parts ofsystem 100. For example, bus controller 120 may allow CPU 105 to sendand receive data to and from system random access memory (RAM) memory125 via frontside memory bus 122. Additionally, bus controller 120 mayallow CPU 105 to display information to a user of system 100 through anaccelerated graphics port (AGP) display card 115 by way of AGP bus 130.While not shown in the system architecture diagram of FIG. 1, CPU 105,bus controller 120, RAM memory 125, and other system components may beintegrated into a single motherboard.

System 100 may comprise a high-performance computing system. Forexample, system 100 may comprise a tower or rack server in a demandingbusiness application. System 100 may operate using a relatively highcore operating frequency, such as 3.8 gigahertz. Additionally, system100 may be subject to overheating due to its fast operation or from theenvironmental conditions surrounding system 100. For example, system 100may operate in an environment with limited cooling capabilities.Consequently, a system administrator for system 100 may want to ensurethat critical parts of system 100 are operating within permissibleoperating temperatures, such that system 100 is not overheating.

To monitor the temperatures of different parts of system 100, a designermay implement IC element temperature sensors in numerous parts of system100. As shown in FIG. 1, CPU 105 may incorporate a first temperaturesensor 106, a second temperature sensor 107, and a third temperaturesensor 108. Temperature sensors 106, 107, and 108 may be located inareas of CPU 105 known to generally operate at higher temperatures, suchthat overheating may be a problem. Consequently, temperature sensors106, 107, and 108 may allow a system administrator of system 100 tomonitor the temperature of those parts and take action if they start tooverheat. For example, the system administrator may provide system 100with better cooling or lower the surrounding environment temperature.

FIG. 1 also shows how IC element sensors may be located in areas otherthan just CPU 105. Cache memory 110 may have a temperature sensor 112and RAM memory 125 may have a temperature sensor 126. Temperaturesensors 112 and 126 may inform the system administrator of the operatingtemperatures of cache memory 110 and RAM memory 125. Cache memory 110and RAM memory 125 may be subject to overheating problems or the systemadministrator may just want to monitor their operating temperatures.

Bus controller 120 may have a temperature sensor 121. Temperature sensor121 may indicate the operating temperature of bus controller 120. Forexample, system 100 may transfer a large quantity of data between CPU105, RAM memory 125, Peripheral Component Interconnect (PCI) bus 140,and AGP bus 130. As a consequence of this heavy data transfer, one ormore sections of bus controller 120 may be subject to overheating.Temperature sensor 121, and other multiple sensors similar to it, maymeasure and report the temperatures of bus controller 120.

AGP display card 115 may have a temperature sensor 116. AGP display card115 may comprise an advanced display adapter in system 100 and besusceptible of overheating. For example, AGP display card 115 maycomprise a high-performance graphics card with one or more dedicatedgraphic processors working in tandem with 512 megabytes (MB) of memory.If system 100 runs a graphics-intensive application, AGP display card115 may generate a large quantity of heat. In this situation, a systemadministrator may use temperature sensor 116 to monitor the operatingtemperature of AGP display card 115.

As alluded to above, system 100 in FIG. 1 may have PCI bus 140 coupledto bus controller 120. Also shown in FIG. 1, PCI/ISA bridge 145 maycouple an industry standard architecture (ISA) bus device, such asEnhanced Intelligent Drive Electronics® (EIDE®) device 150 and auniversal serial bus (USB) device 170, to bus controller 120 by way ofPCI bus 140. In various embodiments, storage devices and other types ofperipheral components may have dedicated temperature sensors and becoupled to PCI bus 140 and PCI/ISA bridge 145. For example, in oneembodiment a small computer systems interface (SCSI) device 155 maycomprise an optical storage drive having temperature sensor 152.Temperature sensor 152 may provide a temperature measurement for theoptical storage drive, or any other SCSI device 155, and it may be usedto transmit the temperature to other parts of system 100 via PCI bus140, such as to CPU 105.

In another embodiment, EIDE® device 150 may comprise a hard drive and becoupled to PCI/ISA bridge 145 and bus controller 120 by way of an EIDE®connector and a flat ribbon cable. EIDE® device 150 may have atemperature sensor 151 to monitor the operating temperature of EIDE®device 150 or one of its internal components. Further, in anotherembodiment, USB device 170 may comprise a flash memory drive, a USB hubadapter, or another type of USB device with temperature sensor 168coupled to PCI/ISA bridge 145 by way of a USB port.

Even further, in other embodiments, FIG. 1 illustrates that temperaturesensors 158 and 163 may be implemented in other types of devices havingintegrated circuits. Temperature sensor 158 may be incorporated intolocal area network (LAN) device 160. For example, LAN device 160 maycomprise a network communications card, wherein temperature sensor 158may monitor its operating temperature. Likewise, temperature sensor 163may be incorporated into a PCI device 165 to monitor its operatingtemperature. PCI device 165 may comprise one of a variety of devicesconforming to the PCI standard, such as an interface card for a scanneror some other peripheral device.

The embodiments in the preceding examples discussed for FIG. 1illustrate how different elements in a computer system may benefit fromtemperature measurements from different implementations of IC elementsensors. One should note, however, that the preceding examples representonly a small number of examples and many more variations are possible.For example, system 100 may have more or fewer peripheral components andsuch components may be different than those depicted in FIG. 1.Additionally, each component in system 100 may have one or moretemperature sensors. For example, CPU 105 shows to have threetemperature sensors, 106, 107, and 108 in FIG. 1. However, CPU 105 mayonly have one temperature sensor or it may have ten, twenty, or moretemperature sensors.

As depicted in FIG. 1, individual components incorporating temperaturesensors may be attached to system 100. Such components may be standalonecomponents. In other words, such components may be attached and detachedfrom system 100. For example, USB device 170 may comprise a flash memorystorage device which may be transported to systems other than system100. To illustrate how temperature sensors may be implemented instandalone devices, which may or may not be coupled to a system such assystem 100, we turn to FIG. 2.

FIG. 2 shows an embodiment of an integrated circuit apparatus 200 havingseveral IC element sensors for measuring temperature. As depicted inFIG. 2, apparatus 200 may be an ASIC chip created using a semiconductorsubstrate 216. For example, apparatus 200 may be an ASIC for a vehicle,such as a car or a military jet aircraft. Apparatus 200 may be dividedinto numerous functional areas and comprise numerous components, such asa central processing unit (CPU) 206, random access memory (RAM) 214,cache 222, peripheral input-output 220, and an input-output (I/O) block230. Apparatus 200 may comprise components for translating digital andanalog signals, such as an analog-to-digital (A/D) converter 247 and adigital-to-analog (D/A) converter 246. For example, system 100 may be anASIC for a vehicle emission control unit, with A/D converter 247 and D/Aconverter 246 translating analog signals to and from a spark timingcontrol unit and an oxygen sensor of the vehicle.

Apparatus 200 may also comprise numerous gate arrays located in variousareas of the integrated circuit, such as gate array 212 and gate array226. Such gate arrays may be used in the ASIC to perform simplecomputations or logic functions outside CPU 206, working in conjunctionwith other blocks, such as peripheral input-output 220 and I/O block230.

Numerous I/O pads 218 may be located around the periphery ofsemiconductor substrate 216, providing connection terminals for outsidepower and signal lines to apparatus 200. As depicted in FIG. 2, a powersupply system voltage VDD 202 may be terminated on I/O pad 203 and bedistributed throughout apparatus 200 by numerous metal traces. Forexample, metal trace 210 may supply system voltage VDD 202 totemperature sensor 208 of CPU 206, as well as other temperature sensorsof semiconductor substrate 216. Likewise, a system ground 250 may beterminated to an I/O pad and distributed to the temperature sensors bymetal trace 249.

A designer of apparatus 200 may utilize IC element sensors to measurethe temperature of numerous sections or individual circuits of apparatus200. For example, temperature sensors 208, 223, 221, and 231 may measuretemperatures of CPU 206, RAM 214, peripheral I/O 220, and I/O block 230,respectively. Similarly, temperature sensors 236, 228, and 248 maymeasure temperatures in gate array 226, D/A converter 246, and A/Dconverter 247, respectively.

The IC temperature sensors of apparatus 200 may be used entirely withinapparatus 200, or the sensors may be used to send the temperaturemeasurements outside of apparatus 200. For example, temperature sensor208 may detect when CPU 206 is overheating and cause CPU 206 to operatewith a lower frequency or with reduced features. Alternatively, atemperature sensor 235 located in an auxiliary function block 233 mayserve as a central temperature sensor for apparatus 200 and detect whenapparatus 200 is running too hot. When apparatus 200 starts to overheat,temperature sensor 235 may trigger logic within auxiliary function block233 to start a cooling fan coupled to apparatus 200. For example,auxiliary function block 233 may be coupled to an external relay via oneor more I/O pads 218. Once an overheating condition is detected,auxiliary function block 233 may close a contact of the external relaycausing the cooling fan to turn on and cool apparatus 200.

FIG. 2 illustrates how IC element sensors may be implemented in variousparts of an integrated circuit, so that the device may perform internaland external functions related to temperature. Apparatus 200 may existin many forms in a variety of devices. For example, apparatus 200 may bean integrated circuit in a cellular telephone, a portable computingdevice, a vending machine, a micro-controller, a television, a stereo, avideo camera, an industrial instrument, or any other type of devicewhere measuring temperature of the integrated circuit or surroundingenvironment may be necessary or desired. To see how one may measuretemperature using an IC element temperature sensor, such as a 2-Tsensor, we turn now to FIG. 3.

FIG. 3 illustrates an embodiment of system 300 employing an IC elementsensor 330 for measuring temperature. System 300 has a power supply 310to supply operating power for system 300. As shown in FIG. 3, powersupply 310 may supply power to a pulse module 320. Pulse module 320 maygenerate a single pulse or a series of pulses for IC element sensor 330.In some embodiments pulse module 320 may generate these pulses to chargeIC element sensor 330 to a designated state, such that IC element sensor330 has a certain magnitude of charge. For example, in one embodimentpulse module 320 may apply a 3.3 volt signal to IC element sensor 330until a certain node within IC element sensor 330 reaches a charge of3.1 volts at which time pulse module 320 may remove or uncouple the 3.3volt signal from IC element sensor 330. Alternatively, in anotherembodiment pulse module 320 may apply a certain voltage to IC elementsensor 330 for a set period of time, irregardless of whether or not thenode of IC element sensor 330 has reached a specific voltage. Forexample, pulse module 320 may apply a 5 volt signal to IC element sensor330 for a period of 50 nanoseconds.

Once IC element sensor 330 has been charged to a certain potential stateand the charging source has been removed or uncoupled, a decay module340 may monitor the rate of voltage discharge of IC element sensor 330.In some embodiments, decay module 340 may measure the quantity of timefor the node of IC element sensor 330 to drop from one voltage potentialto another voltage potential. For example, decay module 340 may measurethe amount of time for the voltage potential of the node to drop from3.1 volts to 1.2 volts.

Alternatively, in other embodiments, decay module 340 may measure anumber of decay periods instead of only one. That is to say, decaymodule 340 may measure a series of decay periods following a series ofcharge cycles created by pulse module 320. Monitoring the series ofdecay periods of IC element sensor 330 may allow decay module 340 todetermine the charge decay rate more accurately by obtaining an averagedecay rate, which may help filter out any anomalous decay ratemeasurements leading to inaccurate temperature measurements.

Decay module 340 may transfer the measurement of the decay rate to atemperature calculator 350. When decay module 340 measures only onedecay period, or a relatively few decays periods, decay module 340 maycommunicate to temperature calculator 350 the number of nanoseconds thatthe node of IC element sensor 330 took to drop from a first voltage to asecond. For example, decay module 340 may determine that the nodedropped from 3.1 volts to 1.2 volts in 2.034 nanoseconds and communicatethis quantity of time to temperature calculator 350. In embodimentswhere decay module 340 measures a series of charge decay periods, decaymodule 340 may communicate the rate of decay to temperature calculator350 in the form of a frequency. For example, decay module 340 maygenerate a pulse every time the voltage of the node of IC element sensor330 drops below 1.2 volts, or every time that the node has been chargedto 3.3 volts. Generating pulses in this manner, and communicating thepulses to temperature calculator 350, may result in temperaturecalculator 350 receiving a signal that has a frequency related totemperature. This concept of receiving a signal having a frequencycorresponding to temperature may be better illustrated with a detailedexample.

Suppose that the temperature of the environment surrounding system 300is 80 degrees Centigrade (C). Suppose further that system 300 hasthermally stabilized at a localized temperature of 85 degrees C. At thistemperature, decay module 340 may detect that pulse module 320 chargesIC element sensor 330 at a frequency of 800 megahertz (MHz). If theenvironment surrounding system 300 increases to 95 degrees C., forexample, then system 300 may thermally stabilize at 100 degrees. At 100degrees, decay module 340 may detect that pulse module 320 charges ICelement sensor 330 at a frequency of 1100 MHz.

Temperature calculator 350 may receive the decay rate signal from decaymodule 340 and use it to calculate a temperature. Continuing with ourprevious example, temperature calculator 350 may determine that afrequency of 800 MHz corresponds to 95 degrees C., while 1100 MHzcorresponds to 100 degrees C. Temperature calculator 350 may calculatetemperature in a variety of different ways in different embodiments. Insome embodiments, temperature calculator 350 may consist purely ofhardware elements, while in other embodiments temperature calculator 350may comprise a software algorithm. For example, temperature calculator350 may comprise one or more latch devices coupled to an ElectricallyErasable Programmable Read Only Memory (EEPROM) device. The latch devicemay capture a number in the form of a digitally encoded 16 bit doubleword transmitted from decay module 340, wherein the number correspondsto either the decay rate or a frequency related to the decay rate. Uponcapturing the number, the temperature calculator may use the encodeddouble word to index a pre-encoded temperature corresponding to thevalue of the number. For example, the encoded word transmitted fromdecay module 340 may be “0000010001001100”, corresponding to 1100 MHz.The latch device may capture this binary value, feed it to the EEPROMwhich will then provide an output value of “1100” based upon a table inthe EEPROM. To facilitate this translation, temperature calculator 350may also have other elements to interpolate and/or round the inputtedvalues to match one of the indexed values in the EEPROM.

Alternatively, temperature calculator 350 may comprise a softwarealgorithm or a software algorithm coupled with hardware. For example,decay module 340 may store the number related to the decay rate in amemory device, such as RAM or a latch device. A processor may retrievethis number from the memory device and calculate a temperature basedupon the value. Continuing with the example above, the processorexecuting the software algorithm may retrieve “0000010001001100” fromthe memory device of decay module 340, perform a calculation, anddetermine that the temperature is 100 degrees C.

One may note that not all embodiments will require temperaturecalculator 350. Temperature calculator 350 may be appropriate when atemperature indication is necessary. For example, if a person wants tosee the actual temperature as measured at IC element sensor 330 on adisplay screen or a local readout, then temperature calculator 350 maybe necessary. Some embodiments, however, may not require conversion. Oneembodiment may be where system 300 operates a cooling fan. In thisscenario, decay module 340 may continually measure the decay of ICelement sensor 330 and store a number representing the rate of decay ina memory device. Logic gates may be coupled to one or more bits of thestored number, such that when the stored number reaches or exceeds aparticular value the logic gates may activate the cooling fan. In otherwords, the logic gates may trigger a device in response to a numberrepresenting the decay rate instead of a number representingtemperature, even though both numbers may be related.

Turning now to FIG. 4, we see an embodiment of a circuit 400 to measuretemperature using a 2-T sensor. Circuit 400 may be implemented in anintegrated circuit and represent one specific implementation of pulsemodule 320, IC element sensor 330, and decay module 340 shown in FIG. 3.Generally, circuit 400 may be described by dividing circuit 400 intofour separate functional blocks. The first block may include p-FET 410and n-FET 420, comprising the 2-T sensor. For example, this first blockmay comprise a CMOS transistor pair. The second block may include toggleflip-flop 460, used to generate a pulse for p-FET 410 and n-FET 420. Thethird block may include inverting Schmitt trigger 430, used to detect acharge decay and trigger another pulse from toggle flip-flop 460. Thefourth block may include counter 485 to accumulate the number of pulsesgenerated by Schmitt trigger 430, which may be related to thetemperature of p-FET 410 and n-FET 420.

A system may utilize circuit 400 to measure temperature sincesub-threshold leakage current is related to temperature. Morespecifically, sub-threshold leakage current may be related totemperature and described by the following equation:I=k*ê((−q*Vt)/(a*kb*T)), where ‘q’ and ‘kb’ are physical constants, ‘a’and ‘k’ are device parameters, and ‘T’ is the absolute temperature. Thesub-threshold leakage current may also depend on ‘Vt’, but if theproduct of ‘a’ and ‘kb’ is much larger than ‘q’ the variation of thethreshold voltage may be minimized.

A voltage potential may be applied to p-FET 410 and n-FET 420 in orderto supply the operating power for the sensor. As depicted in FIG. 4, apositive power supply voltage Vdd 405 may be connected to the drainterminal of p-FET 410, while the power supply ground Vss 425 may beconnected to the source and gate terminals of n-FET 420. Applying supplyground Vss 425 to the gate terminal of n-FET 420 will make it operate ina cutoff state. Initial application of supply voltage Vdd 405 and supplyground Vss 425 to p-FET 410 and n-FET 420 may start charging the pair.While not shown in FIG. 4, supply voltage Vdd 405 and supply ground Vss425 may also be used to supply operating power to Schmitt trigger 430,toggle flip-flop 460, and counter 485. After applying initial power totoggle flip-flop 460, output Q′ 450 will go high and reverse bias p-FET410. Note that the gate of n-FET 425 is coupled to supply ground Vss425, essentially keeping n-FET 420 from turning on during normaloperation. Consequently, a charge potential created at node 415 willtend to decrease and approach the potential of supply ground Vss 425whenever p-FET 410 is turned off.

Whenever node 415 goes low, output 435 of Schmitt trigger 430 will gohigh. As noted, upon initial power-up, Q′ 450 will be high, keepingp-FET 410 turned off. Consequently, the potential of node 415 willremain low causing output 435 of Schmitt trigger 430 to remain high. Inthis phase of operation, output 435 will apply a high to toggleflip-flop 460 clock input 440 and a corresponding inverted input (low)to clear input 445. Stated differently, a high output 435 will partiallyenable toggle flip-flop 460 while a low output 435 will disable andclear toggle flip-flop 460. Toggle flip-flop 460 may stay in this state,with Q′ 450 high, until triggered or activated by applying a high topreset signal line 490 and T input 455.

When T input 455 goes high, and clock input 440 is also high, toggleflip-flop 460 will change states, send Q′ 450 low, and apply a low tothe gate of p-FET 410. Applying a low to the gate of p-FET 410 willcause it to be forward biased and increase the voltage of node 415. Asnode 415 becomes charged from this increase in voltage, the charge willincrease past an upper threshold voltage of Schmitt trigger 430 causingoutput 435 to go low. Sending output 435 low will apply a low to clockinput 440 and clear toggle flip-flop 460 due to the corresponding highapplied to clear input 445. Upon clearing toggle flip-flop 460, Q′ 450will transition high and reverse bias p-FET 410. Reverse biasing p-FET410 isolates supply voltage Vdd 405 from node 415.

With node 415 isolated from supply voltage Vdd 405, the chargeaccumulated at node 415 will tend to dissipate through n-FET 420 due toleakage current flow. As the charge of node 415 dissipates, the chargewill decrease past a lower threshold voltage of Schmitt trigger 430causing output 435 to go high again. As noted, sending output 435 highwill apply a high to clock input 440 and remove the high applied toclear input 445. Assuming the preset signal line 490 and T input 455 areboth still high, toggle flip-flop 460 will change states and Q′ 450 willtransition low forward biasing p-FET 410. Once p-FET 410 becomes forwardbiased, supply voltage Vdd 405 will again increase the voltage of node415. Once the voltage of node 415 passes the upper threshold voltage ofSchmitt trigger 430, output 435 will again transition low. This processof charging, isolating, and discharging node 415 will continue as longas the preset signal line 490 and T input 455 remain high.

The repetitive charging and discharging of node 415, with the associatedtransitions of output 435 for Schmitt trigger 430, will create a seriesof pulses that may be tallied with counter 485. As noted the presetsignal line 490 will be high during operation of circuit 400. When thepreset signal line 490 is high, counter 485 will be enabled and resetinput 480 will be low. Whenever clock 465 is high, the successive pulsescreated by the transitions of output 435 will cause AND gate 470 toapply successive pulses to counter input 475, incrementing counter 485.Arranged in this fashion, one may use counter 485 to count the number ofsuccessive discharges of node 415 during a clock cycle.

As noted previously, the rate of current leakage may depend upon thetemperature of the integrated circuit containing p-FET 410 and n-FET420. This rate of current leakage will affect the rate at which Schmitttrigger 430 and output 435 transition high. As a consequence, thetemperature of the integrated circuit containing n-FET 420 willdetermine the number that counter 485 captures during a clock cycle. Forexample, if the temperature of circuit 400 is 100 degrees C. and output435 creates a pulse train having a frequency of 1100 MHz, a 10 MHz clock465 would cause counter 485 to count up to 110 during a clock cycle.Another circuit may be coupled to circuit 400, pull this number fromcounter 485, and be used to calculate that the temperature is 100degrees C. In other words, this circuit may determine that the count of110 pulses corresponds to the temperature of 100 degrees C.

Circuit 400 is one embodiment of a 2-T temperature sensor circuit. Othercircuit arrangements with alternate circuit elements are possible andmay produce similar results. As depicted in FIG. 4, the embodiment ofcircuit 400 uses Schmitt trigger 430 to detect the successive chargingand discharging of node 415. In alternative embodiments, one may chooseto use a voltage comparator or other device. Additionally, instead ofusing a toggle flip-flop 460, another type of cycling device such as aJ-K flip-flop may be used instead. As for counter 485, alternativeembodiments may use different devices to determine the decay rate ofnode 415. For example, some embodiments may utilize a device thatcalculates the frequency based upon the time between the successivetransitions instead of by counting the transitions for a certain period.

In further embodiments, one may arrange and/or operate p-FET 410 andn-FET 420 differently, including different voltage levels for powersupply voltages Vdd 405 and Vss 425. For example, one may periodicallymanipulate the gate of n-FET 420 instead of having it connected directlyto ground. In another embodiment, one may use two n-FETs instead of onen-FET and one p-FET. In even further embodiments, one may choose othertypes of semiconductor elements, such as a JFET. As the abovealternative embodiments demonstrate, one may substitute differentelements to perform substantially equivalent functions.

FIG. 5 depicts a flowchart 500 illustrating an embodiment of a method tomeasure temperature in an integrated circuit. Flowchart 500 begins withapplying a first voltage to a gate of a first transistor to forward biasthe first transistor (element 510). For example, one may apply a voltagepotential of 3.3 volts to a gate of a p-FET, where the p-FET is coupledin series to an n-FET at a node.

After forward biasing the first transistor (element 510), an embodimentaccording to flowchart 500 may continue by increasing the voltage of thenode coupled to the first and second transistors (element 520).Continuing with the example above, voltage potential of the nodecoupling the p-FET and the n-FET may start increasing as a result offorward biasing the p-FET. After the increasing the voltage of the nodeso that the node has a certain charge, a second voltage may be appliedto the gate of the first transistor to reverse bias it (element 530).For example, the previously applied voltage of 3.3 volts may be removedfrom the gate of the p-FET and replaced by a voltage of 1.1 volts.

Upon charging the node of the first and second transistors (elements510, 520, and 530), a method according to flowchart 500 may continue bymeasuring a rate of the voltage decay of the node (element 540). Forexample, one may determine that charge or voltage potential decreasesfrom 2.9 volts to 1.8 volts in 20 nanoseconds. By measuring this decayrate, one may calculate the associated leakage current rate from whichtemperature may then be inferred (element 550).

One skilled in the art of integrated circuit design will readilyappreciate the flexibility and benefits that the aforementioned examplemethods and apparatuses for measuring temperature in integrated circuitsafford the field of integrated circuits. The specifically describedexamples are only a few of the potential arrangements wherein thetemperature sensors, such as the 2-T sensor, may be operated tocalculate the temperature in various types of integrated circuits.

It will be apparent to those skilled in the art having the benefit ofthis disclosure that the present invention contemplates methods,apparatuses, and systems that may measure temperature in integratedcircuits. It is understood that the form of the invention shown anddescribed in the detailed description and the drawings are to be takenmerely as examples. It is intended that the following claims beinterpreted broadly to embrace all the variations of the exampleembodiments disclosed.

Although the present invention and some of its advantages have beendescribed in detail for some embodiments, it should be understood thatvarious changes, substitutions and alterations can be made hereinwithout departing from the spirit and scope of the invention as definedby the appended claims. Further, embodiments may achieve multipleobjectives but not every embodiment falling within the scope of theattached claims will achieve every objective. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods and steps described in the specification. As one ofordinary skill in the art will readily appreciate from the disclosure ofthe present invention, processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped that perform substantially the same function or achievesubstantially the same result as the corresponding embodiments describedherein may be utilized according to the present invention. Accordingly,the appended claims are intended to include within their scope suchprocesses, machines, manufacture, compositions of matter, means,methods, or steps.

1. A method of measuring temperature in an integrated circuit, themethod comprising: charging at least one of a first transistor and asecond transistor, wherein the first transistor is coupled to the secondtransistor, wherein further a first gate of the first transistor isarranged to have a substantially constant bias voltage; monitoring adissipation of the charge of the at least one of the first transistorand the second transistor; determining a rate of voltage decay basedupon the charge dissipation via leakage current of the first transistor;and deriving a temperature based upon the rate of voltage decay.
 2. Themethod of claim 1, further comprising applying a low voltage to a secondgate of the second transistor to charge a node between the firsttransistor and the second transistor.
 3. The method of claim 2, furthercomprising applying a high voltage to the second gate of the secondtransistor to turn off the transistor.
 4. The method of claim 1, furthercomprising applying a high voltage to a second gate of the secondtransistor to charge a node between the first transistor and the secondtransistor.
 5. The method of claim 1, wherein charging at least one of afirst transistor and a second transistor comprises applying a series ofpulses to a second gate of the second transistor.
 6. The method of claim5, wherein deriving a temperature based upon the rate of voltage decaycomprises calculating the temperature based upon a total number of decaytimes from the series of pulses.
 7. An apparatus for measuringtemperature in an integrated circuit, the apparatus comprising: a pulsemodule to charge a node of a first IC element and a second IC elementcoupled together in series, wherein the second IC element is arranged toremain in a cutoff state while the apparatus operates; a decay module tomeasure a rate of decay of the charge of the node, wherein the rate ofdecay is related to the temperature and related to leakage current ofthe second IC element; and a temperature calculator to calculate thetemperature based upon the rate of decay.
 8. The apparatus of claim 7,wherein the first IC element and the second IC element comprise a CMOStransistor pair.
 9. The apparatus of claim 7, wherein the pulse modulecomprises a flip-flop.
 10. The apparatus of claim 9, wherein theflip-flop comprises a toggle flip-flop.
 11. The apparatus of claim 7,wherein the decay module comprises a Schmitt trigger.
 12. The apparatusof claim 7, wherein the decay module comprises a voltage comparator. 13.The apparatus of claim 7, wherein the temperature calculator comprises acomputing module coupled to a counting module.
 14. An integrated circuitto measure temperature, comprising: a temperature sensor, comprising ap-FET and an n-FET coupled together in series; a pulse circuit coupledthe temperature sensor, wherein the pulse circuit is arranged to chargea node of the temperature sensor; a voltage detection circuit coupled tothe node, the voltage detection circuit to detect when the chargereaches a threshold value; and a temperature circuit coupled to thevoltage detection circuit, the temperature circuit to determine atemperature based upon a rate of the charge reaching the thresholdvalue, wherein the rate of the charge depends upon leakage current ofone of the p-FET and the n-FET.
 15. The integrated circuit of claim 14,wherein the pulse circuit comprises a flip-flop.
 16. The integratedcircuit of claim 15, further comprising a Schmitt trigger coupled to theflip-flop.
 17. The integrated circuit of claim 14, wherein the voltagedetection circuit comprises an inverting Schmitt trigger.
 18. A systemcapable of measuring temperature in a component of the system,comprising: a power supply; an integrated circuit coupled to the powersupply; and a temperature measurement module, wherein the temperaturemeasurement module comprises: a first transistor coupled to a secondtransistor in series; a charging circuit to charge at least one of thefirst and second transistors; a voltage sensing element coupled to atleast one of the first and second transistors, the voltage sensingelement arranged to detect when the charge decays below a thresholdvalue from leakage current of at least one of the first and secondtransistors; and a temperature calculator to calculate the temperaturebased upon a rate of the charge decaying to the threshold value.
 19. Thesystem of claim 18, wherein the temperature calculator comprises asoftware algorithm to calculate the temperature based upon a frequencygenerated by the voltage sensing element.
 20. The system of claim 18,wherein the system comprises one of a personal computer, a servercomputer, an industrial computer, a point-of-sale computer, a videodisplay adapter, an audio system, an ASIC of a vehicle, and a portablemultimedia device.